Extrusion apparatus utilizing an extruder screw housed in an extrusion cylinder are well-known in the art. In U.S. Pat. No. 3,577,588, for example, the material to be treated is conveyed according to FIG. 1 to two funnel-shaped hoppers. The two-sided, axially movable extruder screw then conveys the material from the sides of the extrusion cylinder to its center, where the material is discharged. As described by the foregoing Patent, there is in normal operation an equilibrium of forces in the two sections of the extrusion cylinder supported by a hydraulic system. Therefore, the screw is usually located in a center position without being acted upon by any one-sided axial pressure stress. If there occurs a greater pressure on one side of the cylinder than on the other, for instance, because of the increasing resistance of the supplied material to be extruded, then the screw shifts slightly. In the range of the up to now generally occurring pressures in extrusion apparatuses of 5 to 50 MPa, because of the provided screw having increasing pitch towards the center of the cylinder, the differential force resulting from the disequilibrium of the pressure acts mainly as tractive force of the screw and less as axial compressive force and is at a level which the known designs of axial thrust bearings can absorb without any problems. If an increased differential force results from the mentioned pressure conditions, then the hydraulic system acts on the screw with an axially directed equalization force, which offsets the differential force and is absorbed by a pivot representing the connecting element between the rotating and shiftable worm shaft, as well as the hydraulic cylinder which can only be moved back and forth. The pivot connecting the screw and the hydraulic cylinder comprises conventional axial thrust bearings and a radial bearing. When the equalization force corresponds to the occurring differential force, the screw slides again back into the center position.
The described extrusion apparatus has the definite disadvantage that is does not provide thermoplastic polymers or materials with the higher orientations that can be attained at pressures of 300 to over 1000 MPa, because the extrusion apparatus and its practical operation are unsuitable for such pressure conditions. The shown simple conveyance of material through the funnel-shaped hoppers results in different degrees of loading on each side of the extrusion cylinder. At high pressures, these loadings generate extraordinarily great differential forces, which cannot be absorbed by conventional axial thrust bearings in a pivot. Consequently, the known extrusion apparatus is subject to break down at least at its axial thrust bearings. Furthermore, the disclosed working method does not have the qualities which would make possible the build-up of the intended high pressures in the extrusion cylinder.
Furthermore, there is known a method for pressing plastic masses, particularly acrylonitrile polymer products, in a moldable state, at a pressure of up to 5000 MPa, through a nozzle (DE-OS No. 2,161,182). This method allows attaining high degrees of orientation of the polymers. However, the method allows only a discontinuous working method, which makes industrial treatment of plastic masses uneconomical.